Tcl/Tk 8.6.9 (followed by Tk 8.6.9.1) was released recently. Among other things, they contain fixes for various issues on macOS, some of which have been seen by macOS users of IDLE and other tkinter apps, so the macOS installer should definitely be updated for 3.7.2, 3.6.8, and 2.7.16.

... and master.
I believe for Windows the policy has been to stick with one tcl/tk version for a Python version. But I don't know that this is written on stone. If not too much trouble, I would like master updated occasionally during the a1 period rather than just once around b1. I am not sure about backports.

I pushed the raw Tcl and Tk sources for 8.6.9.0 to cpython-source-deps, but it looks like we need some patches to be able to build on Windows (the X11 headers #define some names that the Windows headers want to use as struct members).
So far I've needed to #undef and redefine None and ControlMask around #include <Windows.h> in winmain.c and tkWin.h, but I think that will be enough.

Probably. I'm 99% sure it's a problem with the latest build tools, and nothing to do with Python. Though I haven't checked out whether we're injecting any compile time flags that may be causing extra things to be included - I have no idea why X11 is necessary, for example.

Thank you both for the updates. After I wrote my previous message, I realized that there is a difference between updating tcl/tk to take advantage of bug fixes (after testing for regressions), and enhancing tkinter to give directly access to new tk features from Python. The latter can still be deferred to the next version.

See discussion in Issue35485. Regressions were found on macOS with Tk 8.6.9.1 and with the more recent Tk 8.6 maintenance branch top of trunk. So for python.org macOS installers, we have reverted to Tcl/Tk 8.6.8. Windows builds will continue to use 8.6.9 unless problems are found.